A laser is a light amplifying apparatus which is capable of producing coherent monochromatic light having an excellent directivity. A dye laser belongs to the class of lasers known as liquid lasers and its basic constitution is an optical resonator including a transparent cell which contains a solution of a laser active dye and a pumping energy source which is optically coupled to the cell. In order to avoid any optical inhomogeneity, the dye solution is usually caused to circulate through a circulation system including the cell during laser operation.
The dye laser requires a pumping energy source for its operation. Sources which emit high-energy electrons or light are employed, such as discharge tubes, flash lamps, liquid lasers (e.g., dye laser), gas lasers (e.g., N.sub.2 or Ar laser), metal vapor lasers (e.g., copper vapor laser), and solid lasers (e.g., Nd-YAG laser). As a result of their pumping action, the dye molecules in the dye laser are excited to higher-energy states, causing radioactive transformation. The produced light which travels along the axis of the resonator is confined within the resonator for a sufficient period of time to cause a strong interaction with the excited dye molecules.
When the number of excited molecules exceeds that of the molecules in the ground state, induction emission occurs and the light is amplified within the resonator to emit laser light.
One of the major advantages of the dye laser over solid and gas lasers is its tunability with respect to output wavelengths. That is, although the laser active dye has a certain range of fluorescent band, its output wavelengths are accurately controlled with the aid of a suitable device such as a prism or a diffraction grating.